1. Field of the Invention
This invention relates to an active matrix substrate for use in active matrix-type liquid crystal displays, image sensors, three-dimensional integrated circuits, etc.
2. Related Background Art
The conventional active matrix substrates have the structure described in, e.g., Japan Display '86, 1986 issue, ps. 196 to 199. FIG. 2 schematically shows its generalized structure. FIG. 2A is a top view of the generalized structure, and FIG. 2B is a sectional view along the line A--A' in FIG. 2A. There are formed a source region 202 and a drain region 203 of a polycrystal silicon thin film having impurities added as donors or acceptors, on a substrate of glass, quartz, sapphire or others. In contact with them are provided a data bus 103 and a picture element electrode 197. A semiconductor layer 206 of a polycrystal silicon thin film is formed in contact with the source region 202 and the drain region 203 to connect both regions 202; 203. A gate insulating film 111 is formed to cover these elements. In contact with the gate insulating film 111 there is provided a gate electrode integrated with a scanning line 101.
But the conventional thin film transistor has the following problems.
Because the data bus 108 and the picture element electrode 107 are provided adjacent to each other, the defect of short-circuits between the data bus 108 and the picture element electrode 107 has frequently taken place due to defective photoresists, etc. in photolithographing.
Furthermore the intersection between the data bus 108 and the scanning line 101 is insulated by one layer of the gate insulating film 111. When a defect, such as a pin hole, or others, takes place, the data bus 108 and the scanning line 101 are short-circuited, and resultantly required data signals and scan signals cannot be supplied to the thin film transistor. In the case the conventional active matrix substrate is applied to an active matrix-type liquid crystal display, this causes line defects on the display screen, with resultant problems that the display quality is much lowered; that data cannot be accurately displayed; that the yield of the active matrix substrate is lowered; that the defect inspection on the active matrix is essential, which much increases the cost; and other problems.